This invention relates to improved means for indicating registration of printed matter on a web or in a multi-color printing press or when the web makes multiple passes through a single cylinder press. It relates more particularly to an improved register target for printing on the web selvage of a web passing through a multi-color printing press in order to verify that the various press cylinders are in alignment during a press run.
Conventionally, a target such as a line or cross is printed by each print cylinder on the web selvage. If all of the cylinders are in register, the different colored crosses or lines printed by the cylinders are all superimposed. However, if a particular cylinder is out of register with the first or reference cylinder, the colored cross or line printed by that cylinder is offset from the others and will readily be visible. When that condition is observed by the operator, he can then retard or advance that cylinder or shift it axially to effect registration.
The prior register targets are disadvantaged, however, in that one cannot tell by observing them the amount by which a particular print cylinder is out of register. Therefore, several attempts may be required to correctly shift the cylinder to correct the registration error. Also if the web segment being examined is severed from the remainder of the web or otherwise loses its known orientation, the observation of the registration targets on that segment may not necessarily tell the operator the direction of the registration error. That is, the design being printed on a web may be nondirectional, e.g. polka dots and if, as happens, the usual targets are printed on both web selvages, one cannot tell from observing a segment of that web which edge was the right hand edge going through the press. Therefore one cannot determine from observing the out-of-register targets on that segment in which directions to make the corrections to restore registration. Therefore, the aligning of print cylinders by superpositioning different colored known registration targets on a web selvage may take a relatively long time, thereby causing excessive wastage of web.